The latest report has found that by releasing an additional 450 gigalitres the environmental benefits would improve, particularly for the Murray, its main tributaries, the Coorong wetlands, lower lakes and Murray mouth.

It says more water would inundate those areas for longer periods.

South Australia has threatened to take a case to the High Court unless more water is returned to the environment under the final Murray-Darling plan.

"We have always known that the proposed 2,750 gigalitres was simply not enough for a healthy river," he said.

"This is why we demanded this modelling be undertaken."

Mr Weatherill said his Government might drop its legal threat if the Federal Government adopts the new modelling.

"There are a number of important conditions that we need to put on this. We need to make sure that that water is delivered in a way that actually maximises the benefits for South Australia so there are a number of key conditions we have on that number, but you need that number first," he said.

"This is now the number that we need to campaign for to get a healthy river.

"We've always stood up for this river, it's now the turn of those who've done the damage to remedy the damage, that's our claim. We're confident that the Commonwealth can meet that demand and we're making that demand of the Commonwealth and the next few weeks are going to be critical in terms of delivering on this plan."

Mr Weatherill said he knew there would be upstream complaint about the latest data.

"There will be people upstream who will fight against this. You've already heard them come out offering any number of excuses about why this shouldn't happen," he said.

"We now know that the issue that was offered as an excuse for not getting water down this river has been blown away by this modelling.

"The notion that you can't get extra water down this river because of the constraints of the river is gone."

The SA Liberal Opposition said it supported the latest flow modelling.